Non-SCV Carb Explanation

[adamscm]

Hello All, I know this topic is ancient, and I've asked related questions before, but this has to do with Loadomatics and Spark Control Valves. I've read all the technical literature on scv's and how you must have them with a LOM distributor. I've experimented with THREE scv carbs on my 144---Holley 1909, Autolite 1100, and Holley 1940. All worked, but either felt underpowered or had a hesitation at take-off. I currently run a NON scv Holley 1940, which seems to work great! At idle, there is no additional advance (I have initial set at eight). Then upon throttle opening, advance shoots up and stays up during higher rpm's. No spark knock. When I DO try the scv carbs, and open the throttle, initially there is no advance, but then it goes up as vacuum and rpm's increase. According to the literature, that's what it's kind of supposed to do--I've read that with load (open throttle, low rpm) you shouldn't have advance because of the lean mixture.
No matter what the experts say, the car runs sweetly with the non-scv 1940. Anyone else have this experience?? In the non-scv 1940, where is the vacuum coming from (Venturi?)? Thanks

 

[bubba22349]

If that Holley 1940 is a later style without a SCV then it's should have a ported vacuum source, with the carb off you can see were the vacuum source is coming from. This would be Manifold vacuum taken from above the throdle plate and at idle speed there is little or no vacuum signal at the carb's port. As to the hesitation your experiencing with the other SCV carb's I would run more base timing of at least 10 to 12 degrees (and sometimes you could need more), then reset your idle rpm to lean best idle, reset the curb idle, and make sure the accelerator pump is working correctly i.e. The Timing and duration of the pump shot. Good luck

 

[hotroady]

As RPM increase, vacuum goes down, not up. I plugged the proper ports in my Autolite 1100, and run ported vacuum to a recurved '67 distributor. Very responsive, 15.8 initial timing with my 65 automatic
idles well at 500rpm in gear. Use 91 octane ethanol free gas. MSD, Pertronix, Crane 91LX coil with resistor wire bypass make it happen.